Mostly Chinese greens, in my experience. As a very generalized rule, the Japanese ones tend to be vaguely greenish, Chinese yellow, and Indian greens slightly brownish/orangeish. Of course, you'll probably find a little bit of every color from every region.

You know, I think terroir has something to do with the final liquor color, but processing probably has the larger input. The greenest Japanese teas are the ones that have been shaded (the leaves produce more chlorophyll this way) and they do so much chopping and steaming and...stuff...that it just makes my head spin. The Chinese don't typically shade their teas, and seem to have much less steps to their processing to boot. As far as the Indians...well, I have a feeling that most Indian greens I've tried have actually been very lightly oxidized oolongs. They just have that oolong taste to me.